Boson Jonas, Johansson Lennart, Ramebäck Henrik, Agren Göran
Swedish Defence Research Agency, FOI CBRN Defence and Security, SE-901 82 Umeå, Sweden.
Radiat Prot Dosimetry. 2009 Jun;134(2):122-9. doi: 10.1093/rpd/ncp079. Epub 2009 May 8.
Semi-empirical methods are often used for efficiency calibrations of in situ gamma-ray spectrometry measurements with high-purity germanium detectors. The intrinsic detector efficiency is experimentally determined for different photon energies and angles of incidence, and a suitable expression for the efficiency is fitted to empirical data. In this work, the combined standard uncertainty of such an efficiency function for two detectors was assessed. The uncertainties in individual efficiency measurements were found to be about 1.9 and 3.1% (with a coverage factor k = 1, i.e. with a confidence interval of about 68%) for the two detectors. The main contributions to these uncertainties were found to originate from uncertainties in source-to-detector distance, source activity and full-energy peak count rate. The standard uncertainties of the fitted functions were found to be somewhat higher than the uncertainty of individual data points, i.e. 5.2 and 8.1% (k = 1). With the introduction of a new expression for the detector efficiency, these uncertainties were reduced to 3.7 and 4.2%, i.e. with up to a factor of two. Note that this work only addresses the uncertainty in the determination of intrinsic detector efficiency.
半经验方法常用于用高纯锗探测器进行的现场伽马射线能谱测量的效率校准。针对不同的光子能量和入射角，通过实验确定探测器的本征效率，并将效率的合适表达式拟合到实验数据。在这项工作中，评估了两个探测器的这种效率函数的合成标准不确定度。发现两个探测器各自效率测量的不确定度分别约为1.9%和3.1%（包含因子k = 1，即置信区间约为68%）。这些不确定度的主要来源是源到探测器距离、源活度和全能峰计数率的不确定度。发现拟合函数的标准不确定度略高于单个数据点的不确定度，即5.2%和8.1%（k = 1）。通过引入探测器效率的新表达式，这些不确定度降低到3.7%和4.2%，即降低了多达一半。请注意，这项工作仅涉及探测器本征效率测定中的不确定度。
